Method and system for handling a network-identified emergency session

ABSTRACT

The invention relates to a method and system for establishing an emergency session in a communication system which includes at least one user equipment and one or more network entities involved in establishing an emergency session. When the user equipment initiates a session by sending a message to a network entity indicating an identifier, e.g. the call number or logical name of a called entity, one of said network entities analyses the received identifier. When detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the latter that the initiated session is an emergency session. The user equipment thereupon initiates the execution of an emergency session. Thus, even when the user equipment is unable to detect, by itself, that the intended session is an emergency session, the network will inform the user equipment on the emergency session for ensuring appropriate handling thereof.

FIELD AND BACKGROUND OF THE INVENTION

The invention generally relates to the connection of emergency sessions such as emergency calls.

Emergency calls shall be supported in IP Multimedia networks (IMS). The UE (User Equipment) may usually be able to indicate in the initial session setup (e.g. in the INVITE message of SIP) that the session is an emergency session.

However, there may be situations where the initial session setup message is just sent with an ordinary number and there is no indication about the emergency. These situations may e.g. occur when a subscriber is roaming in another IMS network.

It is important to identify the intended emergency session as soon as possible, because the network and the UE need to perform some special actions for performing the emergency session.

SUMMARY OF THE INVENTION

The present invention provides method and system for enabling emergency sessions to be established in a reliable manner.

The invention provides a method and/or system as defined in the claims.

This invention discloses means and functions of how the network can detect an emergency session, how the UE can be informed about it and what effects this information has on later session setup.

The invention provides among others a Network-identification of an emergency session initiated by a session initiating entity such as a user equipment (UE) including mobile or stationary stations or terminals, or the like.

Even when the user equipment is unable to detect by itself that the initiated session is an emergency session, it is quickly informed thereon and can then initiate the appropriate steps for establishing the emergency session.

According to a first embodiment of the invention, in order to guarantee resources at the transport level for the emergency call, a response is sent back to the UE immediately after a control means such as P-CSCF has discovered that the session is an emergency session. When the UE receives such a response it will perform a normal emergency session procedure, e.g. as defined in 3GPP specifications. To execute a normal emergency session, the UE will e.g. obtain or query location information and send it in the INVITE message and also the UE will activate an emergency PDP context for the session.

The invention enables to identify the session to be an emergency session as soon as possible so that the network and the UE can perform the necessary special actions for the emergency session as quickly as possible.

In one of the alternative implementations of the invention, the control entity such as P-CSCF does not respond immediately to UE when it has received an INVITE message from the UE but waits for the reception of a message, e.g. 183 Session Progress, from an emergency center or an intermediate network entity, and adds to that message the emergency information.

The information about the emergency call is not delayed at all, and the call establishment is continued in the conventional or any other manner such as with the 183 Session Progress message.

Sending an INVITE message takes remarkable radio resources and it is not preferable to send multiple INVITE messages. Actually there is no delay in session establishment, since UE has not yet started creating secondary PDP Context before UE receives the SDP message. This means that the indication can be included with high priority for the user plane. If no emergency centre is indicated, a default emergency center may be chosen.

This invention concerns a situation, in which PDP context activation can not or will not be performed at first when initiating a session for any reason, but a message such as an INVITE message is sent first from the UE to the CSCF.

Further details, aspects and advantages of the invention will become apparent from the following reference to specific embodiments and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a method and system in accordance with the present invention;

FIG. 2 shows a second embodiment of a method and system in accordance with the present invention;

FIG. 3 illustrates a third embodiment of a method and system in accordance with the present invention;

FIG. 4 shows an implementation for emergency session processing in a normal case.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

This invention discloses solutions to several problems such as:

-   The UE is able to activate an emergency PDP context after it has     been informed about the session characteristics. This is important     to get high priority for the PDP context in the GPRS (General Packet     Radio Service) and RAN (Radio Access Network). -   The UE sends location information after it is being informed about     the session characteristics (it is assumed that location information     is not sent in every INVITE message). The location information is     used for selecting the most suitable Emergency Centre (EC).

FIG. 1 shows an embodiment of the invention which includes a call originating element, i.e. a session initiating element, such as a mobile station (UE) 10, and a network which comprises a serving network element such as a Serving GPRS Support Node (SGSN), and a further control element such as a Call State Control Function (CSCF) or Proxy Call State Control Function (P-CSCF) 11. The further network elements necessary for completing an IP multimedia session such as a terminating element, a gateway node if needed, a subscriber information register such as a home location register (HLR) or home subscriber server (HSS), etc. are known to the skilled man and are therefore neither shown nor described in more detail. Generally, a MSC (Mobile Switching Centre, not shown) may return to UE a Call Proceedings message which contains a Priority information field defining also EC (Emergency Centre).

In all embodiments described above or below, the UE 1 may be equipped with a USIM (User Services Identity Module).

The embodiments shown in FIGS. 1, 2, and 3 relate to a Network-identified emergency session.

A solution to guarantee resources at the transport level to perform the emergency call is to respond back to the UE 10 immediately after a network entity, e.g. a control means such as P-CSCF 11, has discovered that the session is an emergency session. When the UE 10 receives the response, i.e. is informed, by the network, on the initiated session being an emergency session, it will perform normal emergency session procedure, e.g. as defined in 3 GPP specifications.

FIG. 1 shows the solution at a general level.

In step 1, the UE 10 sends a session initiation message, e.g. an INVITE message of SIP (Session Initiation Protocol), which indicatess an identifier, e.g. the E.164 number or LN (logical name), of the called entity, to the P-CSCF 11.

In a step 2, the P-CSCF 11 analyses the number or LN. When detecting that a normal session is to initiated, a normal connection procedure is continued. When, however, the P-CSCF 11 discovers that the call is emergency call, steps 3 to 6 shown in FIG. 1 are performed.

In step 3, a response is sent to the UE 10 indicating that the session is an emergency session.

Step 4: The UE 10 returns an acknowledgement message ACK to the P-CSCF 11.

In an optional step 5, the UE 10 may inform the user that the session is emergency session, e.g. by displaying an appropriate message on a display of the UE 10.

Then, a normal emergency session is executed (performed) as indicated by step 6. The execution of a normal emergency session means that the UE 10 will e.g. obtain location information and send it in the INVITE message and also that the UE 10 will activate an emergency PDP context for the session.

The response message at step 3 can be a new message, or an existing SIP message or other known message can be used. The information in the response message may be a new parameter in SIP protocol, but an existing parameter may also be used.

FIG. 2 shows a solution in which, in step 3, a SIP 302 message “Moved Temporarily” is used as response. The parameter value in the 302 message indicates that the session is an emergency session. The parameter may e.g. be “Contact: sip:emergency@visited.cscf.com”. This value can e.g. be used in SIP URI when sending a new INVITE message to P-CSCF 11, or the UE 10 just generates a new INVITE message with the indication of an emergency session. Another alternative can be to use the SIP NOTIFY method.

Apart from the above discusion, the embodiment shown in FIG. 2 has the same structure and functioning as the one of FIG. 1.

FIG. 3 illustrates another embodiment of the invention. In addition to the UE 10 and the P-CSCF 11, a Serving CSCF (S-CSCF) 12 and an Emergency Centre (EC) 13 are shown. The embodiment according to FIG. 3 provides an alternative functioning as compared to the embodiments of FIGS. 1 and 2.

In order to achieve a very fast session establishment the P-CSCF 11 does not respond back to the UE 10 immediately after P-CSCF 11 has discovered that the session is an emergency session. On the contrary it continues session establishment and optionally, if possible, the P-CSCF 11 adds an indication of emergency session to the messages generated by P-CSCF 11 for ensuring high priority treatment of the messages.

The details of the procedure are shown in FIG. 3. Taking account of the nature of emergency session it is highly desirable not to add any additional delay also in case of abnormal situations to session establishment. By using the alternative of FIG. 3, it is possible to avoid the transfer of another INVITE message over the air interface, which is probably the largest and slowest message and thus very time-consuming.

The response message (in SIP, preferably a message “183 Progress”) to the UE 10 preferably includes an indication of emergency session. This allows to activate an emergency PDP context for the session.

If there should not exist location information in S-CSCF 12 (or the relevant server) to select an emergency center 13, the S-CSCF 12 (or relevant server) will select an emergency center 13 without location information of the user (e.g. it selects a default emergency center, nearest emergency center or it may use some other technique to select the emergency center e.g. based on the address of P-CSCF 11.

As shown in FIG. 3, in step 1, the UE 10 initiates a session establishment and sends a session setup message, e.g. an INVITE message, to the P-CSCF 11. The P-CSCF 11 analyses the number or logical name (LN) of the called party/entity indicated in the session setup message, and discovers that the call is an emergency call. The P-CSCF 11 may add an indication of emergency session to the INVITE message (it is also possible that other elements add this indication of emergency session to the INVITE message).

In step 2, the INVITE message is forwarded to the S-CSCF 12.

In Step 3, the S-CSCF 12 selects an emergency center (EC) 13 and forwards the INVITE message to the EC 13.

Step 4: The EC 13 responds to the INVITE request by returning a response such as SIP 183 “Session Progress” to the S-CSCF 12. The subset of the media flows shown in steps 4 to 6 indicates that messages are returned back to originating endpoints proposing an EC 13 for providing support, or requesting the emergency session.

Step 5: The S-CSCF 12 forwards the response such as SIP 183 “Session Progress” back to the P-CSCF 11.

Step 6: The P-CSCF 11 forwards the response such as SIP 183 “Session Progress” back to the UE 10. The response includes the indication of emergency session. The UE 10 thus learns that this session is an emergency session and can act properly.

The circles and ovals shown in FIG. 3 mean “Emergency call detected, Possibility to add an emergency indication”.

FIG. 4 presents a proposal for normal emergency session establishment for the case where the UE has USIM. It is assumed that the UE has activated a signalling PDP context to the GGSN in the visited PLMN.

In the following, the steps shown in FIG. 4 are described in more detail, referring to the step numbering of FIG. 4.

-   1. UE may request SAI (Service Area Identity) from SGSN. -   2. SGSN sends response message to UE. -   3. UE sends the SIP INVITE request, containing an initial SDP, to a     P-CSCF determined via the CSCF discovery mechanism. Information     about emergency call is sent in the INVITE message. UE includes the     location information in the INVITE message. -   4. P-CSCF detects that the call is an emergency call using the     information in the INVITE message e.g. by analysing the number or     name requested. P-CSCF selects a S-CSCF in the visited network and     forwards the SIP INVITE request including the information about     emergency call to S-CSCF. -   5. S-CSCF uses the location information to select an appropriate EC.     S-CSCF forwards the request to EC. -   6. The media stream capabilities of the destination are returned     along the signaling path. -   7. S-CSCF forwards the message containing the destination SDP     cababilities to P-CSCF. -   8. P-CSCF authorizes the resources necessary for this session. -   9. P-CSCF forwards the SDP message to the originating endpoint. -   10. UE decides the final set of media streams for this session, and     sends the Final SDP to P-CSCF. -   11. P-CSCF forwards the final SDP to S-CSCF. -   12. S-CSCF forwards this message to EC. -   13. Activate PDP Context Request. The UE activates a PDP context for     the emergency session by sending the Activate Secondary PDP Context     Request message to the SGSN. The UE indicates that the PDP context     is used for an emergency session. For the PDP context, the     Allocation/Retention Priority shall be at once set to the high     value. -   14. The SGSN, when recognising that the PDP context is for an     emergency session, may itself request location information from     SRNC, in order to receive updated or more accurate location     information regarding the UE. SGSN thereafter sends a location     report to Gateway Mobile Location services Centre (GMLC) as     specified in TS 23.271, and the EC may obtain this location     information from GMLC. -   15. Radio Access Bearer Setup -   16. Create PDP Context Request -   17. Create PDP Context Response -   18. Activate PDP Context Accept -   19. UE sends the “Resource Reservation Successful” message to the     terminating endpoint, via the signaling path established by the     INVITE message. -   20. P-CSCF forwards this message to S-CSCF. -   21. S-CSCF forwards this message to EC. -   22. Resources are reserved successfully. -   23. EC sends information about alerting to S-CSCF. -   24. S-CSCF forwards the Ringing message to P-CSCF. -   25. P-CSCF forwards this message to UE. -   26. EC answers the call and sends final 200 OK message to S-CSCF. -   27. S-CSCF forwards final 200 OK message to P-CSCF. -   28. P-CSCF indicates the resources reserved for this session should     now be committed. -   29. P-CSCF forwards final 200 OK message to UE. -   30. UE starts the media flow for this session. -   31. The calling party responds to the 200-OK final response with a     SIP ACK message which is sent to P-CSCF. -   32. P-CSCF forwards the SIP ACK message to S-CSCF -   33. S-CSCF forwards the ACK message to EC.

Although the invention has been described above with reference to specific embodiments, the scope of protection of the invention intends to cover all modifications, omissions, additions and amendments of the disclosed features as well.

The teaching according to the invention is preferably implemented in an All-IP Network but may also be employed in networks of various other types, i.e. in IM, GPRS and UMTS domains. 

1. A method for establishing an emergency session in a communication system which includes at least one user equipment and one or more network entities involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, an information is sent to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein, when the network entity detects that the session to be initiated is an emergency session, an emergency center is informed on the emergency session to be established, and said information is returned to the user equipment only after receipt of a response from the emergency center, the emergency session then being established between the user equipment and the emergency center.
 2. A method of claim 1 comprising a further step wherein the user equipment initiates the execution of an emergency session upon receipt of said information sent to the user equipment for informing the user equipment that the initiated session is an emergency session.
 3. Method according to claim 2, wherein the execution of the emergency session includes the step of obtaining location information of the user equipment and of sending the location information to one of the network entities.
 4. Method according to claim 2, wherein the execution of the emergency session includes the step of activating an emergency Packet Data Protocol, PDP, context for the session.
 5. Method according to claim 1 wherein the information returned to the user equipment is a message which includes a parameter indicating an address of a network entity to be addressed for establishing an emergency session.
 6. Method according to claim 1, wherein the identifier of the called entity is the call number or logical name of the called entity.
 7. Method according to claim 1, wherein the network entity analysing the received identifier is a Call State Control Function (CSCF).
 8. A method for establishing an emergency session in a communication system which includes at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the user equipment that the initiated session is an emergency session, comprising a further step wherein the user equipment reinitiates the session by sending a message to the call controlling network, the message comprising said information.
 9. A method of claim 8, wherein the call controlling network element is a P-CSCF.
 10. A method for establishing an emergency session in a communication system which includes at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the user equipment that the initiated session is an emergency session, comprising a further step wherein the user equipment initiates a new session by sending a message to the call controlling network element the message comprising the said information.
 11. A method for establishing an emergency session in a communication system which includes at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the user equipment that the initiated session is an emergency session, comprising the further step of, in response to receiving the information, a network initiating the execution of the emergency session.
 12. A method for establishing an emergency session in a communication system which includes at least one user equipment, at least one call controlling network element involved in establishing an emergency session, and an emergency center, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, the network element sends an information to the emergency center or to an intermediate network element for forwarding the information to the emergency center, said information informing the emergency center on the emergency session to be established, an indication of the emergency session being sent to the user equipment for informing the user equipment that the initiated session is an emergency session.
 13. Method according to claim 12, wherein after receipt of a response from the emergency center, the emergency session is established between the user equipment and the emergency center.
 14. A method of claim 12, wherein the call controlling network element is a P-CSCF.
 15. A communication system for establishing an emergency session, the communication system including at least one user equipment and one or more network entities involved in establishing an emergency session, wherein said user equipment is configured to initiate a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities is configured to analyse the received identifier, when detecting that the session to be initiated is an emergency session, said analysing network entity or another network entity is configured to send an information to the user equipment for informing the latter that the initiated session is an emergency session, wherein the network entity, when detecting that the session to be initiated is an emergency session, is configured to inform an emergency center on the emergency session to be established, and to send said information to the user equipment only after receipt of a response from the emergency center, the emergency session then being established between the user equipment and the emergency center.
 16. A system according to claim 15, wherein the user equipment is configured to initiate, when receiving the information that the initiated session is an emergency session, the execution of an emergency session.
 17. System according to claim 16, wherein the execution of the emergency session includes the step of obtaining location information of the user equipment and of sending the location information to one of the network entities.
 18. System according to claim 16, wherein the execution of the emergency session includes the step of activating ah emergency PDP context for the session.
 19. System according to claim 15, wherein the information returned to the user equipment is a message which includes a parameter indicating an address of a network entity to be addressed for establishing an emergency session.
 20. System according to claim 15, wherein the identifier of the called entity is the call number or logical name of the called entity.
 21. System according to claim 15, wherein the network entity analysing the received identifier is a Call State Control Function (CSCF).
 22. A communication system for establishing an emergency session, the communication system including at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element is configured to analyse the received identifier, wherein, when detecting that the session to be initiated is an emergency session, to send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein the user equipment is configured to reinitiate the session by sending a message to the call controlling network element, the message comprising the said information.
 23. A system of claim 22, wherein the call controlling network element is a P-CSCF.
 24. A communication system for establishing an emergency session, the communication system including at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element is configured to analyse the received identifier, wherein, when detecting that the session to be initiated is an emergency session, to send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein the user equipment is configured to initiate a new session by sending a message to the call controlling network element, the message comprising the said information.
 25. A communication system for establishing an emergency session, the communication system including at least one user equipment and at least one call controlling network element involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element is configured to analyse the received identifier, wherein, when detecting that the session to be initiated is an emergency session, to send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein a network is configured to initiate the execution of the emergency session in response to receiving the information.
 26. A communication system for establishing an emergency session, the communication system including at least one user equipment, at least one call controlling network element involved in establishing an emergency session, and an emergency center, wherein, when said user equipment initiates a session by sending a message to the call controlling network element indicating an identifier of a called entity, the call controlling network element is configured to analyse the received identifier, and, when detecting that the session to be initiated is an emergency session, to send an information to the emergency center or to an intermediate network element for forwarding the information to the emergency center, said information informing the emergency center on the emergency session to be established, an indication of the emergency session being sent to the user equipment for informing the user equipment that the initiated session is an emergency session.
 27. A system according to claim 26, wherein after receipt of a response from the emergency center, the emergency session is established between the user equipment and the emergency center.
 28. A system of claim 27, wherein the call controlling network element is a P-CSCF.
 29. A method for establishing an emergency session in a communication system which includes at least one user equipment and one or more network elements involved in establishing a session, wherein, when said user equipment initiates a session by sending a message indicating an identifier of a called entity, one of the network elements analyses the identifier of the message, and, when detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the user equipment that the initiated session is an emergency session, comprising a further step wherein, the user equipment initiates the execution of an emergency session upon receipt of said information informing the user equipment that the initiated session is an emergency session.
 30. The method of claim 29, wherein the user equipment informs a user of the user equipment that the session is an emergency session.
 31. The method of claim 30, wherein the user equipment informs the user that the session is an emergency session by displaying a message on a display of the user equipment.
 32. The method of claim 29, wherein the user equipment sends an acknowledgment message to the call controlling network element in response to the information returned to the user equipment for informing the user equipment that the initiated session is an emergency session.
 33. The method of claim 29, wherein the call controlling network element is a Proxy Call State Control Function, P-CSCF.
 34. A communication system for establishing an emergency session, the communication system including at least one user equipment and one or more network entities involved in establishing a session, wherein said user equipment is configured to initiate a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities is configured to analyze the received identifier, when detecting that the session to be initiated is an emergency session, said analyzing network entity or another network entity is configured to send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein the user equipment is configured to initiate, when receiving the information that the initiated session is an emergency session, the execution of an emergency session.
 35. The communication system of claim 34, wherein the user equipment is configured to inform a user of the user equipment that the session is an emergency session.
 36. A user equipment comprising: means for sending a message to a network entity for initiating a session, the message indicating an identifier of a called entity; means for receiving, when the session to be initiated is an emergency session, an information informing the user equipment that the initiated session is an emergency session; and means for initiating the execution of an emergency session upon receipt of said information.
 37. The user equipment according to claim 36, wherein the execution of the emergency session includes the step of obtaining location information of the user equipment and of sending the location information to a network entity.
 38. The user equipment according to claim 36, wherein the execution of the emergency session includes the step of activating an emergency PDP (Packet Data Protocol) context for the session.
 39. The user equipment according to claim 36, wherein said information is a message which includes a parameter indicating an address of a network entity to be addressed for establishing an emergency session.
 40. The user equipment according to claim 39, wherein said message is a SIP (Session Initiation Protocol) message.
 41. The user equipment according to claim 36, wherein the identifier of the called entity is the call number or logical name of the called entity.
 42. The user equipment according to claim 36, wherein the user equipment comprises means for informing a user that the initiated session is an emergency session.
 43. The user equipment according to claim 36, wherein the user equipment is configured to send an acknowledgment message to a call controlling network element in response to receiving the information informing the user equipment that the initiated session is an emergency session.
 44. The user equipment according to claim 36, wherein the user equipment, in order to guarantee that an established emergency call has enough network resources, initiates the execution of a new emergency session upon receipt of said information.
 45. A method for establishing an emergency session in a communication system which includes at least one user equipment and one or more network elements involved in establishing a session, wherein, when said user equipment initiates a session by sending a message indicating an identifier of a called entity, one of the network elements analyses the identifier of the message, and, when detecting that the session to be initiated is an emergency session, an information is always returned to the user equipment for informing the user equipment that the initiated session is an emergency session, in order to guarantee that the emergency session to be established has enough network resources.
 46. A network element for use in a communication system, wherein the network element is adapted to: receive a message from a user equipment initiating a session, the message indicating an identifier of a called entity; analyze the identifier of the message; and, when detecting that the session to be initiated is an emergency session, to always return an emergency session information to the user equipment for informing the user equipment that the initiated session is an emergency session.
 47. The network element according to claim 46, wherein the network element is a call controlling network element.
 48. A communication system for establishing an emergency session, the communication system including at least one user equipment and one or more network entities involved in establishing a session, wherein said user equipment is configured to initiate a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities is configured to analyze the received identifier, when detecting that the session to be initiated is an emergency session, said analyzing network entity or another network entity is configured to always send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, in order to guarantee that the emergency session to be established has enough network resources.
 49. A method for establishing an emergency session in a communication system which includes at least one user equipment and one or more network entities involved in establishing an emergency session, wherein, when said user equipment initiates a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities analyses the received identifier, and, when detecting that the session to be initiated is an emergency session, an information is sent to the user equipment for informing the user equipment that the initiated session is an emergency session, wherein the user equipment sends an acknowledgment message to a call controlling network element in response to receiving the information informing the user equipment that the initiated session is an emergency session.
 50. User equipment comprising: means for sending a message to a network entity for initiating a session, the message indicating an identifier of a called entity; means for receiving, when the session to be initiated is an emergency session, an information informing the user equipment that the initiated session is an emergency session; and means for sending an acknowledgment message to a call controlling network element in response to receiving the information informing the user equipment that the initiated session is an emergency session.
 51. A communication system for establishing an emergency session, the communication system including at least one user equipment and one or more network entities involved in establishing an emergency session, wherein said user equipment is configured to initiate a session by sending a message to a network entity indicating an identifier of a called entity, one of said network entities is configured to analyse the received identifier, when detecting that the session to be initiated is an emergency session, said analyzing network entity or another network entity is configured to send an information to the user equipment for informing the user equipment that the initiated session is an emergency session, and wherein the user equipment is configured to send an acknowledgment message to a call controlling network element in response to receiving the information informing the user equipment that the initiated session is an emergency session. 